1. Field of the Invention
The present invention relates generally to the field of bio-electrochemistry and more particularly to electrochemical synthesis bioreactors.
2. Description of the Prior Art
Living organisms transfer electrons through their electron transport chains as the core of their most basic metabolism. In aerobic organisms, oxygen is used as the final electron acceptor when it is combined with carbon to form carbon dioxide (CO2). It has been shown that certain microbes are capable of depositing electrons onto other substances besides oxygen. The metal reducing bacteria are an example of this phenomenon in nature in that they utilize oxidized metals such as Fe (III) as a final electron acceptor. The ability of these and other microbes to directly deposit electrons onto electrodes, or onto intermediates which interact with the electrodes, is exploited in the Microbial Fuel Cell, (MFC). Among the many types of microbes capable of obtaining energy this way are those of genus Geobacter and Shewanella. It is also speculated that this phenomenon, referred to as ‘exoelectrogenicity’ is a characteristic of many species and does not have a strong corollary to phylogeny.
A less well understood natural phenomenon is the oxidation of inorganic compounds as a way for living organisms to derive energy. Such Chemoautotrophs obtain energy from the oxidation of inorganic compounds and obtain carbon from the fixation of carbon dioxide. Chemoautotrophic bacteria include nitrifying bacteria, sulfur-oxidizing bacteria, iron-oxidizing bacteria, and Knallgas-bacteria and Purple nonsulfur bacteria such as rhodobacter capsulatus which oxidize hydrogen. More recently it has been shown that some bacteria are able to either directly or indirectly derive energy via the uptake of electrons from electrodes supplying DC current. Microbes that fix carbon from CO2 and obtain energy from electricity are known herein as electro-autotrophs. Energy can be obtained by some microbes by accepting an electron, while other microbes obtain energy by donating an electron.
In both the deposition and uptake of electrons, organisms rely on chemical carriers with specific oxidation or reduction potentials to pass the electrons from one to another while extracting energy to create new chemical bonds. In photosynthesis, for example, electrons from water, excited by light energy, are transferred through a variety of carriers and this energy is captured by being used to strip the carbon atom from CO2 and bond it to another carbon. In heterotrophic organisms, electron transport is the method by which the energy contained in carbon-carbon bonds is harvested for use, as carbohydrates are broken during respiration. In the case of aerobic organisms, oxygen serves as the final electron acceptor when it is combined with carbon to form CO2.